1. Field of the Invention
The invention relates generally to building systems, and more particularly, to a method and apparatus for the construction of insulated walls from pourable building material, such as concrete, using a one-sided insulated formwork.
2. Discussion of the Related Art
Conventional formwork used in the construction of walls from pourable building material (e.g., pourable concrete) consist of two opposed wall panels (typically, plywood) connected by a rod, trusswork or other variety of connecting structure. The pourable building material is poured into the space (or cavity) formed between the opposed wall panels. As the building material is poured and subsequently cures, the panels are maintained in a fixed spaced relation by the connecting structure.
In recent years, it has been found desirable to use an insulating material for formwork wall panels for providing thermal and acoustic insulation to the finished wall. In the case of formwork used in the construction of concrete walls, the wall forms using an insulating material are commonly known as Insulated Concrete Formwork (ICF). The ICF is constructed into walls by stacking individual ICF components (sometimes referred to as blocks) to build an insulated wall form, which remains as a permanent part of the finished wall. After the building material has cured, the insulated wall panels are not removed from the cured wall surface as is the case with conventional plywood forms. Typically, the ICF component includes two insulating wall panels made of a foamed polymeric material such as plastic.
In certain applications, it is desirable to remove one of the walls while leaving the other wall in place after the building material has cured. For example, a builder may wish to have an exposed outer surface of concrete, or building codes may require that insulating material not be exposed to external elements as this material may have an unacceptable rate of degradation over time. In one known approach, builders will simply tear off the soft insulating material after the building material has cured. This technique is disadvantageous as it wastes material and adds to the cost associated with the cleanup and disposal of the non-reusable material. Another similar approach is found in U.S. Pat. No. 5,065,561 to Mason. Mason discloses removing one or both panels of a formwork (each panel being either foamed plastic panel or a plywood panel) via a frangible connection. Mason's formwork consists of slotted panels slid onto shanks integrally formed at each end of a connecting structure in the form of a bridge. After the concrete has cured, one or both of the panels are removed by breaking the bridge along a score line. This technique for removing panels is also disadvantageous. The web must be broken to disconnect the panel, which can be labor intensive and results in wasted material. Mason does not teach how to remove panels for formwork having a portion of the connecting structure molded into the insulating panels, such as the formwork described in U.S. Pat. Nos. 5,390,459, 5,567,600, and 5,809,727 to Mensen, the disclosures of which are incorporated by reference herein in their entirety.
European Publication 0591080-A1 of Gantan Beauty Industry Co. (Gantan) teaches a method for constructing walls using a formwork with a heat insulating member, surface side form, and back side form interconnected using a threaded socket assembly. In contrast to Mason, Gantan removes the back side form by disengaging the socket assembly (the back side form is therefore removable). However, Gantan suffers from numerous drawbacks, including the requirement that a surface pressure means and surface side form must be applied to the exterior surface of the insulating panel to provide the necessary strength for reacting pressure forces exerted by the curing concrete.
U.S. Pat. No. 4,426,061 to Taggart discloses a formwork for forming insulated walls consisting of an exterior form panel connected to an insulation panel using a T-shaped screw, brackets and spacer element positioned between the two panels. In similar fashion to that of Gantan, Taggart teaches a method for removing the form panel and suffers from the drawback of requiring externally applied end caps, retainer pieces and cross beams to provide the necessary strength for reacting pressure forces exerted on the insulating panel by the building material. The formwork systems in both Gantan and Taggart are additionally undesirable because the formwork support must be constructed on-site. Construction time and labor costs are increased, as are the number of components and complexity of the formwork due to the complicated, multi-part mechanical structure required by these types of systems.
Supporting structures are needed in ICFs to reinforce the insulating panels which have a low stress tolerance relative to conventional non-insulating material (e.g., plywood) used in conventional formwork panels. Accordingly, when insulating material is used, ICFs will typically require either an externally applied surface side form (as taught in Gantan), an end cap, retainer piece and cross beam (as taught in Taggart), a tie and fastening ends with sliding engagement with the panel (as taught in Mason), or a panel with molded-in supporting structure (as taught in Mensen). In each of these prior formworks, the additional reinforcing structure is necessary for distributing the load across a surface area of the insulating panel to reduce stress concentrations. None of the prior systems having a removable panel provide the advantages inherent in using an internal reinforcement for the insulating panel, such as taught in aforementioned patents to Mensen.
It is sometimes desirable to use an ICF which has two, reinforced insulating panels connected using a tie releasably engageable with each panel along its respective inner bearing surfaces (i.e., the surface of the panel which comes into contact with the poured concrete). These types of ICF systems are commercially available and are disclosed for example, in U.S. Pat. No. 4,229,920 to Lount and U.S. Pat. No. 5,701,710 to Tremelling. Tremelling and Lount each describe an ICF that provides a pre-reinforced insulating panel and a means for selectively choosing the wall thickness on site. These types of ICF also tend to reduce shipping costs because the panels and ties can be shipped separately and stored in a reduced volume, but typically are more costly overall due to increased on-site labor required to construct the forms. In addition, the structural integrity of each form is dependent upon the skills of the on-site laborer, unlike the ICFs completely assembled by the manufacturer, such as the ICF's taught in the aforementioned Mensen patents. None of the known ICF systems having a removable tie employ an ICF that includes a removable panel for use as a one-sided form.
As a result of the foregoing drawbacks and limitations in existing formwork systems, there exists a need for insulated formwork with a conveniently removable panel and reinforced insulating panel that does not require the on-site construction of externally applied supporting structure to reinforce the insulating panel. In particular, the existing formwork systems do not address the need for reducing the labor and material costs associated with detachment of the removable panel while avoiding the drawbacks of constructing complicated and labor intensive structural supports for the insulating panel on site. For example, it would be desirable to have a connecting structure for a one-sided insulated form that provides structural support to the insulating panel without the need for cross-beams, end caps or surface side forms, that also avoids having to break the form to remove a panel or requires complex connecting structure to facilitate detachment of the removable panel. There is also a need for a one-sided ICF system employing a removable tie and/or panel connecting structure where the provision of a variable wall thickness at the job site is also desirable.